Added some defaults to make sure Exercise is off by default

mod/exercise/defaults.php

@@ -0,0 +1,9 @@
+<?php  // $Id$
+    if (empty($CFG->exercise_initialdisable)) {
+        if (!count_records('exercise')) {
+            set_field('modules', 'visible', 0, 'name', 'exercise');  // Disable it by default
+            set_config('exercise_initialdisable', 1);
+        }
+    }
+
+?>